The Evolved Packet Core (EPC) architecture is a mobile network architecture defined by the 3rd Generation Partnership Project 3GPP) in TS 23.401, and mainly includes network elements such as a packet data network gateway (PGW), a mobility management entity (MME), and a policy control and charging rules function entity (PCRF). The PGW, as an interface gateway between an EPC network and a packet data network (PDN) that provides services, is responsible for forwarding and filtering user data flows, allocating user IP addresses, executing quality of service (QoS) policies and charging, or the like. The MME is mainly responsible for user mobility management, user attachment signaling processing, or the like. The PCRF makes a decision on a policy and charging control (PCC) rule according to user access network information (which is acquired from a Gx interface), an operator policy (which is locally configured), user subscription data (which is acquired from a user subscription database), information (which is obtained from an Rx interface) about an ongoing IP multimedia subsystem (IMS) service of a user or the like, and provides the rule to the PGW for execution, thereby implementing policy and charging control. The PCC rule includes IP flow description information (such as source and destination addresses of an IP packet and source and destination port numbers), an execution policy corresponding to the IP flow description information, QoS information (such as a priority and a bandwidth), access control information (forward/discard), charging information, and the like.
The 3GPP has further defined Single Radio Voice Call Continuity (SRVCC) in TS 23.216. SRVCC is used to resolve an issue about continuity of a voice call when a user equipment (UE) switches between different access technologies, and a process of switching, by the UE, from a circuit switching (CS) domain of a 2G/3G network to a packet switching (PS) domain of a 3G/LTE network is described. That is, the UE uses an IMS voice service in the CS domain of 2G/3G access defined by the 3GPP; and when the UE moves out of coverage of the CS domain or a signal of the CS domain is relatively poor, the UE switches to the PS domain of 3G/LTE access and continues to use the IMS voice service through the PS domain. A basic principle of switching the IMS voice service from the CS domain to the PS domain is as follows: The UE completes IMS registration in the PS domain beforehand, and negotiates information, such as an IP port on a UE side for performing the voice service in the PS domain, with an IMS network; when the UE is ready to switch IMS from the CS domain to the PS domain, a mobile switching center (MSC), which is a core network element in the CS domain, notifies an MME in the PS domain that switching will occur soon, so that the MME performs resource allocation beforehand; and at the same time, the MME interacts with the IMS network to acquire an IP port number of an IMS network side that the IMS network allocates for the to be switched, and sends the IP port number to the UE. In this way, the UE may send or receive an IMS voice data packet after being attached to a PS network, thereby ensuring continuity of the IMS voice service.
A specific process of switching the IMS voice service in an SRVCC scenario includes step S101 to step S116, which are described in the following.
S101. A base station controller or a radio network controller sends a switching request to the MSC.
S102. The MSC interacts with a device on the IMS network side and acquires an IP port number (media ports) allocated by the device on the IMS network side.
S103. The MSC sends a switching request for switching the UE from the CS domain to the PS domain to a destination MME or a destination SGSN, and the destination MME or the destination SGSN acquires an indication from the CS domain.
S104. The destination MME or the destination SGSN sends a context request to a source MME or a source SGSN.
S105. The source MME or the source SGSN returns a response of the context request to the destination MME or the destination SGSN.
S106. The destination MME or the destination SGSN completes resource reservation on a PS network side.
S107. The destination MME or the destination SGSN returns a response of the switching request for switching the UE from the CS domain to the PS domain to the MSC.
S108. The MSC returns the response obtained in step S107 to the UE.
S109. The MSC sends a session transfer preparation request to the device on the IMS network side, and the device on the IMS network side stops sending a voice service packet to the CS domain and starts sending a voice service packet to the PS domain, where a source port of the packet is an IP port allocated by the device on the IMS network side, and a destination port of the packet is an IP port of the UE side negotiated beforehand between the UE and the device on the IMS network.
S110. The UE switches to the PS domain.
S111. The source MME or the source SGSN notifies the MSC that “the UE has been attached to the PS domain”.
S112. The destination MME or the destination SGSN notifies a PGW in the PS domain that “the UE has completed the CS-to-PS switching”.
S113. The PGW interacts with a PCRF to activate a PCC rule on a default bearer.
The PCC rule activated on the default bearer is used to temporarily transmit the IMS voice service during the switching from the circuit switched domain to the packet switched domain.
S114. The destination MME or the destination SGSN sends a context acknowledgment message to the source MME or the source SGSN.
S115. The source MME or the source SGSN interacts with the base station controller or the radio network controller to release resources.
In steps S116 to S117, the UE interacts with the device on the IMS network side, notifies the device on the IMS network side that the switching is completed, and the device on the IMS network side triggers the PS domain to create a dedicated bearer for the IMS voice service of the UE, thereby ensuring quality of service of the IMS voice service.
As can be seen from the preceding switching process, in the process of switching the IMS voice service of the UE from the CS domain to the PS domain, the PCRF installs a PCC rule on the PGW for the default bearer so as to temporarily transmit the IMS voice service. After the dedicated bearer is established for the IMS voice service, that is, after step S117 in the preceding process is performed, all data packets of the IMS voice service start to be sent on the dedicated bearer and the PCC rule on the default bearer is no longer valid; and for resource saving reasons, the PCC rule on the default bearer should be deleted.
A method for deleting the PCC rule on the default bearer provided in the prior art is implemented on a basis of a timer mechanism. That is, a timer is simultaneously started when the PCRF or the PGW installs the PCC rule on the default bearer for the IMS voice service switching from CS to PS; and when a preset duration of the timer expires, the PCC rule on the default bearer is deleted.
In many scenarios, it cannot be predicted when the device on the IMS network side triggers the PS domain to create the dedicated bearer for the IMS voice service of the UE, and therefore actually the timer duration cannot be accurately preset in the prior art. As a result, if the preset timer duration is excessively short, the PCC rule on the default bearer is deleted before a dedicated bearer is created for the IMS voice service of the UE and the UE cannot receive a data packet; or if the preset timer duration is excessively long, an invalid PCC rule stays on the PGW for a long time, thereby causing a resource waste.